Premium Rapid Resizer subscribers can download designs from the page where you enter your design's size. There's a Download button farther down it.
Click Download Design. If your design is already an SVG (from the letter stencil maker, the Designer, or an uploaded SVG file), it will download as that.
Otherwise, it will download as a PNG. You can upload your PNG at https://online.rapidresizer.com/tracer.php to vectorize it into an SVG, though results may vary.